Antenna



W. B. NOWAK A N 25 mm ANTENNA Falled Dec. 9, 1944 WELI/ILLE Patented Apr. 25, 195% iii ANTENNA Welville B. Nowak, Boston, Mass, assignor, by

mesne assignments, to the United States of" America as represented by the Secretary of War Applicationxflecember 9, 19.44, Serial No. 567,404

7 Claims. l

The present invention relatesto an antenna for use with a high frequencycommunication system. The invention is particularly directed to an an tenna having a parabolic reflector adapted to radiate electromagnetic energy in a highiy directional bearnwhich is adapted to scan through space in a conical or other desiredmanner.

Such scanning may be obtained by rotating the antenna feed and its radiatinguelement rela-- tive to the axis of a fixed reflector, or by rotating the reflector itself. to employ an antenna in which the feed elements It has been found desirable.

remain fixed so that thepolarization axis of the feed-radiated energy remains constant. With the polarizationlaxis maintained. constant, it has been determined that the. over-all effective range of a system is somewhat higher than it is with rotating types of feed elementsin which the axis.

of polarization rotates.

One of the objects of the present invention is to provide an antenna having a fixed element for feeding energy and which is adapted to radiate a rotating beam of energy with its-axis of polar-- ization maintained constant.

It is also an object of the invention to providev means for radiating constantly polarized electromagnetic waves in a narrow beam which scansa field in space in a: conical or the like manner. It is another object ofthe invention to provide a hollow wave guide through which energy is transmitted. which guideis in fixed position rela tive to parabolic reflector and which has a rotating end wall provided with an orifice through which energy may be radiated toward the parabolic reflector.

It is still another-object .of the invention to provide a simple and inexpensive radiating antenna having the above type of radiationpattern together with a satisfactory gain characteristic.

Further objects and advantages of the invention will become apparent as the description proceeds. reference be'mg made to theaccompanying drawingsin which:

l is a side elevation view, partly broken of the antenna embodying the present. invention with a parabolic reflector shown diagran matically;

2 is a front elevation view, partly broken away, of the antenna embodyingthe present invention, looking in the directionifrom the parr abolic reflector, of Fig. 1;

Fig. 3 is a side elevation view, partly broken away, of an antenna similar to Fig. 1 showing a different manner of. connection toxa feed transmission line;

Fig. l is a front elevation view, broken away, of a modified type of radiating orifice according to the present invention;

Fig. 5 is a sectionalview along the line 55 of Fig. 4.

In the drawings, 10 indicates a. parabolic re.- fiector of an antenna-system. Suitably mounted in front of the reflector ill isa. chamber or hollow wave guide it disposed with its longitudinal axis substantially colinear with the axis of reflector it. Wave guide 5 1 maybe ofany desired shape or dimension suitablefonbeing excited by high frequency energy. However, it is preferable that wave guide 1 comprise a low Q type chamber, or

, be of relatively. largedimension and preferably rectangular in shape, as shown.

Energy is fed tothe guide it in any suitable manner, for example, by means of a transmission line l2. Line izmay be a wave guide or a coaxial type transmission line suitably coupled to wave guide I i so that energy transmitted from a source (not shown) through transmission line 92 will properly excite wave guide H. As indicated in Fig. 1, transmission. line 271s shown as a Wave guide entering wave guide It centrally through one end thereof.

Fig. 3. shows a transmission line i3 entering the wave guide it through one of the side walls thereof with one endof the guide Ii formed as a movable tuning plunger l t for impedance matching. It will be understood that when the transmission line isthe coaxial-cable type, provision. is made for suitably coupling the cable to the wave guide, forexample, by a, probe or by coupling the outer. conductor of the coaxial cable to the wave guide wall and extending the center conductor throughthe-wave guide-so that the center conductor acts as anantenna or exciting probe.

At the end of the wave gu de I l nearer to the parabolic reflector l0; inFigs. 1 and 3, a substantially circular disc I5 is rotatably mounted. The center of disc -55 lies on the axis. of the reflector. The disc l5 is rotatable about the axis of the reflector in aplane through the focal point of, and perpendicularto the axis of, the reflector it. Any desired means may be provided for permitting the disc IE to rotate, for example by providing a ball-bearing raceway, generally indicated at It. Thedisc may be rotated in any suitable manner, for example, by providing a ring gear i! mounted on the peripheral portion of the disc 15 and driven by crown gear 58 and actuated through shaft I9 by motor. 20.

Disc 15 is provided .with a circular orifice-2| disposed off-center with respect to its axis of rotation. When the wave guide ii is properly excited, energy is radiated through orifice 2i toward the parabolic reflector l8, and therefore the orifice 2! is the source of illumination of the reflecting parabola. As orifice 2! is off-center with respect to the axis of the reflector Hi, the beam of energy radiated from orifice 25 toward the reflector it will be directed from the reflector at an angle with the reflector axis. As the disc rotates, the beam will describe in space the surface of a cone.

In order that proper excitation and radiation be obtained, the orifice 25 must be approximately half the operating wave length in diameter. As noted above, the wave guide ii is preferably of relatively large dimension with respect to the orifice and should comprise a low Q chamber. The axis of polarization of the energy in chamber or wave guide H is constant, determined merely by the excitation of the wave guide itself. Therefore, the polarization of the radiated beam is independent of the position of orifice 2!, so that a constantly polarized beam will be obtained. If the chamber or wave guide H is properly designed, wave guide I! and the exciting element constituting the orifice 2! will be desirably broadbanded. Accordingly, critical adjustments will not be necessary for small changes in the frequency of the feed energy.

With the simple orifice or aperture as indicated in Figs. 1, 2 and 3, there is a tendency for currents to flow on the face of disc l so that illumination of the parabola tends to occur from a relatively large area instead of just from the orifice 2i itself. This tendency may be overcome by providing a radio-frequency choke at the orifice so that the radio-frequency currents for exciting the reflector it are maintained within the orifice 2i, and radiation will be effectively from a small source.

Figs. 4 and 5 show an improved type of orifice, indicating one means for providing such a radio-frequency choke. 55 indicates the rotating disc, and 2! indicates the orifice or aperture as described with reference to Figs. 1, 2 and 3. Suitably mounted on the outside face of disc i5 are two abutting plane members or discs 22 and 23. Disc 22 is provided with an orifice or aperture of substantially larger diameter than the diameter of orifice 2!, and disc 23 is provided with an orifice or aperture having a diameter larger than that of orifice 2!, but smaller than that of the orifice in disc 22. The respective orifices are concentric. Thus, an annular slot is provided between discs I5 and 23 of proper dimensions that it constitutes a choke effective for confining the radio-frequency currents of the radiated energy within orifice 2!.

The above description has been principally directed to an orifice rotatable in a circular path around the axis of the reflector, so that conical scanning will be produced. It will be understood that other forms of scanning can he produced by moving the orifice relative to the axis of the parabola in a noncircular path.

While preferred embodiments of the present invention have been illustrated and described, it will be understood these are capable of modification and improvement without departing from the spirit of the invention. Therefore. it is not desired that the scope of the invention be limited to the precise details set forth.

What is claimed is:

1. An antenna for a high frequency communication system having, in combination, a reflector, a closed hollow chamber mounted in fixed position in front of said reflector with its longitudinal axis substantially colinear with the axis of said reflector, a transmission line for conducting high frequency energy to said chamber to excite the same, a plane member rotatably mounted in the end of said chamber nearer to said reflector, the plane of said member being substantially perpendicular to said reflector axis and substantially at the focal point of said reflector, said member being rotatable relative to said chamber about said reflector axis, said member being provided with an orifice located off-center with respect to said axis, and. means for rotating said member.

2. In a directional antenna, a reflector, a wave guide associated with and directed at said reflector substantially in the direction of the axis thereof, means for feeding electrical energy to said wave guide, an apertured member disposed in and closing the end of said waveguide adjacent to said reflector and movable in a plane perpendicular to the axis of said wave guide, said aperture in said member being disposed ecceutrically about said axis, whereby there is directed at said reflector upon movement of said member a beam of electrical energy whose source is at said aperture and follows a prescribed path about said axis and in said plane perpendicular thereto, and means coupled to and imparting movement to said member.

3. In a directional antenna, a reflector, a wave guide associated with and directed at said reflector substantially in the direction of the axis thereof, means for feeding electrical energy to said Wave guide, an apertured member disposed in and closing the end of said wave guide adjacent to said reflector and supported for rotation with respect to said wave guide substantially about and in a plane erpendicular to said axis, said aperture in said member being disposed eccentrically about said axis, whereby upon rotation of said member there is directed at said reflector a beam of electrical energy whose source is at said aperture and follows a circular path about said axis in said plane perpendicular thereto, and means coupled to and rotating said member.

a. In a directional antenna, a reflector, a wave guide associated with and directed at said reflector substantially in the direction of the axis thereof, means for feeding electrical energy to said Wave guide, an apertured disc disposed in and closing the end of said wave guide adjacent to said reflector and supported for rotation with respect to said wave guide and substantially about said axis in a plane substantially perpendicular thereto, the aperture in said disc being disposed eccentrically with respect to said axis whereby there is directed at said reflector upon rotation of said disc a beam of such energy whose source is at said aperture and travels in a circular path about said axis, and means for rotating said disc.

5. In a directional antenna, a reflector, a wave guide associated with and. directed at said reflector substantially in the direction of the axis thereof, means for feeding electrical energy to said wave guide, an apertured member extending substantially about and in a plane perpendicular to said axis and movable with respect to said wave guide, said member being disposed in and closing the end of said wave guide adjacent to said reflector, said aperture in said member being disposed eccentrically about said axis, whereby there is directed at said reflector by way of said aperture a beam of electrical energy whose source is at said aperture and follows a prescribed path about said axis and in said plane perpendicular thereto, means connected to said member, for producing a radio-frequency choke surrounding said aperture to prevent radio-frequency currents from flowing over the outer surface of said member, and means coupled to and imparting movement to said member.

6. In a directional antenna, a reflector, a wave guide associated with and directed at said reflector substantially in the direction of the axis thereof, means for feeding electrical energy to said wave guide, a disc disposed in and closing the end of said wave guide adjacent to said reflector and supported for rotation with respect to said wave guide substantially about said axis in a plane substantially perpendicular thereto, said disc being provided with an orifice disposed eccentrically with respect to said axis whereby there is directed at said reflector upon rotation of said disc a beam of such energy whose source is at said orifice and travels in a circular path about said axis, means associated with said disc at said orifice and constituting a radio-frequency choke effective to maintain within said orifice occurring radio-frequency currents and to oppose a tendency for such currents to flow on the surface of said disc, and means for rotating said disc.

7. In a directional antenna, a reflector, a wave guide associated with and directed at said re- 6 flector substantially in the direction of the axis thereof, means for feeding electrical energy to said wave guide, a disc disposed in and closing the end of said wave guide adjacent to said reflector and supported for rotation with respect to said wave guide and substantially about said axis in a plane substantially perpendicular thereto, said disc being provided with an orifice disposed eccentrically with respect to said axis whereby there is directed at said reflector upon rotation of said disc a beam of such energy whose source is at said orifice and travels in a circular path about said axis, two plane members disposed at one and the same side of said disc and each provided with an orifice registering with and of larger diameter than said first-named orifice, the diameter of the orifice in the plane member immediately adjacent said disc being larger than that of the orifice in the other plane member, and means for rotating said disc.

WELVILLE B. NOWAK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,420,264 Rost et a1 May 6, 1947 2,429,601 Biskeborn et al Oct. 28, 1947 

